Why are myPBX U300 incoming calls being dropped?

Question

Telephony

Good afternoon. Please help, I've been fighting with an iron Asterisk in the form of IP ATC Yeastar MyPBX U300 for several days now. The line is up, the outgoing ones go out, there is a voice on the outgoing ones, but the incoming ones are simply stupidly cut off, no beeps, no squeaks, no IVR, tried hundreds of options for outgoing routes, SIP settings, contacted the provider, they say our hardware drops, tried to turn off the farewall completely and on the PBX and on the Mikrotik router. The logs are sort of weird.